In recent years, various functions have been implemented on so-called mobile terminals such as mobile phones and PHS (Personal Handyphone System) terminals. For example, various kinds of functions such as a mail transmission/reception function, an internet access function, a camera function and a music replay function are implemented in addition to an original telephone function. The various kinds of functions and various kinds of operations in the functions can be executed by pressing keys on an operation section provided for the mobile terminal.
However, the number of keys arranged on the operation section of the mobile terminal is usually limited, and a different operation can be therefore instructed by one key in accordance with a type of function to be executed by the mobile terminal. For example, ten numeral keys from 0 to 9 are usually provided as ten keys of the operation section. For example, when the mobile terminal having such ten keys is used to originate a call, each key is used as the numeral key to input a telephone number. In a case of text input, each key is used as a text input key to input Japanese syllabary. Furthermore, in the case of music replay, one key of the ten keys is used for searching of a next music program and another key thereof is used to stop music replay.
The recent mobile terminal is small in size and the operation section of the mobile terminal has keys which are smaller in size. Accordingly, it is almost impossible to write on one key, all of data to instruct operations executable in the functions. In general, a number in a case of use as the numeral key and a character in a case of use as a text input key (i.e. the character “a” is written on a key by which characters in the A row can be inputted) are written on one key. Accordingly, when the music replay function is used, which of the keys should be pushed to stop music replay could not be understood by the user only by seeing what is written on each key. Thus, the mobile terminal instruction manual is commonly used to confirm and determine the operation.
However, it is troublesome for the user of the mobile terminal to confirm instruction contents of the respective keys by referring to the instruction manual. Therefore, the mobile terminal which is easier to see and use keys is proposed in a related art (for example, Japanese Patent Publication (JP 2005-352987A).
Japanese Patent Publication (JP 2005-352987A) discloses a “key input device”. More specifically, in the key input device which allows the characters and/or symbols to be displayed on key tops in an operation panel suitable for small electronic equipments such as a mobile terminal represented by a mobile phone, a switch sheet is arranged on a printed circuit board. An electronic paper is arranged on the switch sheet, and a transparent key sheet having key tops is arranged on the electronic paper. The characters and/or symbols in the key tops are changed by the electronic paper which displays the characters and/or symbols. Therefore, the display of input keys of the electronic equipment can be changed in accordance with a display mode, whereby making it easier to see and use the key input device.
Also, a proposal is made to make it easier for a user of a mobile data terminal to recognize functions assigned to respective operation buttons (or operation keys) in a related art (Japanese Patent Publication JP 2006-191548A).
Japanese Patent Publication (JP 2006-191548A) discloses a “portable data terminal apparatus”. More specifically, the portable data terminal device is provided with operation buttons for displaying operation contents by an electronic paper and a function selecting section adapted to select a function used in the portable data terminal device. A display switch section is also provided to switch the operation contents displayed on the electronic paper in accordance with a function selected by the function selection means. Furthermore, when an use state is changed by changing a way of holding the portable data terminal device (such as changing a way of holding from a longitudinal use to a lateral use), contents suitable for the operation pattern are displayed on the operation buttons. Therefore, operation contents displayed on the operation buttons can be switched in accordance with a function used in the portable data terminal device or a use state, whereby operability is improved.
The key input device according to JP 2005-352987A and the portable data terminal device according to JP 2006-191548A are provided to allow the characters and/or symbols to be variably displayed in individual key tops or key frame outside regions. However, the characters and/or symbols are not displayed outside the key frames. Accordingly, if it is desired to display many characters/symbols in one key frame, a key frame corresponding to each key needs to be made larger to expand a displayable region. It is however difficult to expand the key frame corresponding to each key because each key has a small shape in recent mobile terminals as stated above.
Moreover, JP 2005-210322A discloses a technique to change an exterior design by mounting an electronic paper on an externally exposed portion of a mobile terminal. It may be possible to apply this technique and operate various applications. However, the electronic paper mounted on the externally exposed portion makes it difficult to operate various applications only by dial keys. It is also impossible to cope with complicated functions only by side keys.